PC Proxy: A New Method of Dynamical Tracer Reconstruction

摘要

A detailed development of the principal component proxy method of dynamicaltracer reconstruction is presented, including error analysis. The method worksby correlating the largest principal components of a matrix representation ofthe transport dynamics with a set of sparse measurements. The Lyapunov spectrumwas measured and used to quantify the lifetime of each principal component. Themethod was tested on the 500 K isentropic surface with ozone measurements fromthe Polar Aerosol and Ozone Measurement (POAM) III satellite instrument duringOctober and November 1998 and compared with the older proxy tracer method whichworks by correlating measurements with a single other tracer or proxy. Using a60 day integration time and five (5) principal components, cross validation ofglobally reconstructed ozone and comparison with ozone sondes returnedroot-mean-square errors of 0.16 ppmv and 0.36 ppmv, respectively. This comparesfavourably with the classic proxy tracer method in which a passive tracerequivalent latitude field was used for the proxy and which returned RMS errorsof 0.30 ppmv and 0.59 ppmv for cross-validation and sonde validationrespectively. The method seems especially effective for shorter lived tracersand was far more accurate than the classic method at predicting ozoneconcentration in the Southern hemisphere at the end of winter.